JSON vs XML: Which Is Better and When to Use Each

JSON has largely replaced XML in modern web development, but XML is far from dead. Understanding the differences helps you make the right choice — and work with legacy systems that still rely on XML.

The same data in both formats

<!-- XML -->
<user>
  <name>Alice</name>
  <age>28</age>
  <active>true</active>
  <tags>
    <tag>developer</tag>
    <tag>javascript</tag>
  </tags>
</user>

// JSON
{
  "name": "Alice",
  "age": 28,
  "active": true,
  "tags": ["developer", "javascript"]
}

The JSON version is roughly half the size and arguably more readable.

Key differences

• Size: JSON is typically 30-50% smaller than equivalent XML.
• Readability: JSON is cleaner for most developers. XML is more verbose but self-documenting.
• Data types: JSON has native numbers, booleans, null, arrays. XML represents everything as text — you define types via schema.
• Attributes: XML supports element attributes (<user id="123">). JSON has no equivalent — IDs are just regular keys.
• Comments: XML supports comments. JSON does not.
• Namespaces: XML has namespaces for combining documents from different sources. JSON has nothing equivalent.
• Schema validation: XML Schema (XSD) is mature and powerful. JSON Schema is newer but well-supported.

Where JSON wins

• REST APIs — JSON is the universal language of modern APIs
• JavaScript applications — JSON.parse() is native
• NoSQL databases — MongoDB, DynamoDB, Firestore all use JSON natively
• Configuration files (alongside YAML)
• Smaller payloads over the network

Where XML still wins

• SOAP web services — enterprise systems built before REST existed still use SOAP/XML heavily
• Document formats — Office files (.docx, .xlsx) are XML internally
• RSS/Atom feeds — all RSS feeds are XML
• SVG images — Scalable Vector Graphics are XML
• Android layouts — Android UI is defined in XML
• Legal/financial documents — many regulated industries require XML (XBRL for financial reporting)

Convert between JSON and XML

// JavaScript — json-to-xml (using fast-xml-parser)
import { XMLBuilder, XMLParser } from 'fast-xml-parser';

// JSON to XML
const builder = new XMLBuilder();
const xml = builder.build({ user: { name: "Alice", age: 28 } });

// XML to JSON
const parser = new XMLParser();
const json = parser.parse(xmlString);

# Python
import json, xmltodict

# JSON to XML
data = {"user": {"name": "Alice", "age": 28}}
xml = xmltodict.unparse(data, pretty=True)

# XML to JSON
xml_str = "<user><name>Alice</name></user>"
data = xmltodict.parse(xml_str)
json_str = json.dumps(data, indent=2)